This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
The current invention is applicable for measuring flow rates with ultrasonic transit time technology (e.g., ultrasonic flow meters, or UFM). The application is specifically developed for a flow meter to monitor chemical injection in subsea oil wells (typically injecting mono-ethylene glycol or MEG). This specific subsea application has flow rates that range from 100 liters/hr to 30,000 liters/hr. For this flow range and product viscosity—the Reynolds Number ranges from laminar flow to fully turbulent flow. This range of Reynolds Number produces velocity profiles that vary from parabolic to nearly flat. As a flow meter, the average velocity (e.g. integral of velocity profile divided by the area) must be measured.
The current ultrasonic flow meter arrangement uses in one embodiment two transducers at opposing ends of a pipe/tube where one is upstream from the fluid flow and other is downstream from the fluid flow, both transducers transmit and receive signals. Each transducer generates plane waves into the fluid. The difference in transit times between the upstream and downstream signal is used to calculate the velocity between the two transducers. This difference in transit time reflects the average fluid velocity projected onto the acoustic path.
Unless the transducer is larger than the diameter of the pipe/tube, the acoustic path measures a cross section of velocities that represent an area that is less than the full cross section of the pipe/tube. Only if the transducer is larger than the tube itself can the full cross section be measured. A transducer large enough to completely cover the pipe/tube cross section is not always possible or even practical depending upon the pipe/tube size or pressure (e.g., required wall thicknesses). Some UFM have used multiple bounces; but these multiple bounces cannot get the full cross section.
By measuring the full cross section, velocity profile effects are addressed (for example any distortions due to hydraulics or changes in the velocity profile due to transition from laminar to turbulent).